Quadrapole mass spectrometers are well known in the art. Generally they employ four parallel rods with suitable AC and/or DC voltages applied between pairs of the rods to generate shaped electric fields in the area between the rods. A beam of charged particles to be analyzed is injected into the electric field at one end of the rods. The electric fields serve to filter the particles whereby only particles of selected mass-to-charge ratio exit from the other end. The mass-to-charge ratio, which is passed is determined by the voltages applied to the rods. The particles exiting the rods are detected and an output signal is generated. By scanning the voltages, the output signal represents a spectrum of the masses which are present in the input beam.
In quadrapole mass spectrometers the selectivity and sensitivity of the mass spectrometer is critically dependent upon accurately spacing the rods from one another in both the circumferential and radial directions. In present practice the rods are supported by ceramic mounts located near each end of the rods. The ceramic mounts are machined to provide grooves which receive the rods. The rods are secured to the ceramic mounts by screws. The screws extend through holes in the ceramic mount and into tapped holes in the rods. Machining required both for the ceramic mount and the tapped holes is relatively expensive and is critical to the proper mounting of the rods. Pairs of rods are then interconnected by metal straps or conductors. Hexapole and octapole mass spectrometers are also known. The rod mounts in such mass spectrometers are substantially more complicated and the accuracy of positioning is more critical.